Pest and Disease Control and Management Methods for Garden Plants in Northern Regions

Since urban garden plants need to comprehensively consider ornamental requirements, the inter-regional introduction of garden plants increases the risk of pests and diseases. In addition, the relevant work system framework is imperfect, making it difficult to implement quarantine work effectively, thereby missing the optimal timing for prevention and control, or there are many deficiencies in garden plant pest and disease control work, making it difficult to manage garden plant pests and diseases.

1 Effectively Improving the Quality of Garden Plant Pest and Disease Control in Northern Regions

On the basis of fully analyzing the current status of garden plant pest and disease control work in northern regions, relevant staff should improve the quality of pest and disease control work from all aspects through specific analysis of specific problems.

2 Reasonable Garden Design

Reasonable garden design is an important means of achieving pest and disease control and isolation. It should be understood that the introduction of diverse plants brings threats from various pests and diseases, which will bring additional risks to garden plants. Therefore, when designing gardens, the pest and disease risks faced by different plants should be fully considered, with reasonable planning and through staggered planting methods to better achieve pest and disease control. This is also an important factor that must be considered in garden design work. Taking the urban environment as an example, the combination of trees and shrubs or grasses forms a complex plant community with varying heights, and this complex plant community has a positive limiting effect on pests and diseases.

3 Focus on Species Diversification Construction and Interactions Between Species

The environment in northern regions is dry and cold, and the ecosystem of the garden environment itself is not stable enough, making it prone to pest and disease problems. If plant varieties are diversified and there are significant differences between species, there are often situations where pests and diseases mutually inhibit each other, which is actually beneficial for achieving pest and disease control across the overall plant community. However, some plants grown together often cause pests and diseases, which should be noted. For example, planting pears and Chinese juniper together can cause pear-juniper rust, and planting pines and peonies together can induce pine-peony rust.

4 Strengthen the Construction of Prevention and Control Work Systems

The plant pest and disease prevention and control system is a whole and should be comprehensively constructed to avoid shortcomings. In addition to improving the professional quality of relevant staff, attention to climate conditions should also be an important part of pest and disease control work. Caution should be exercised when using various methods such as physical control, chemical control, and biological control.

July Garden Plant Pest and Disease Forecast for Northern Regions

        July is a season of high temperature and high humidity, and is one of the key periods for pest and disease control.
   I. Garden Plant Pest Forecast
   (1) Scarab beetles and white grubs. In June, various scarab beetles have emerged as adults. Many green spaces planted with cotton rosemallow, zelkova, Chinese parasol tree, Chinese bayberry, firethorn, red maple, etc. have been severely damaged by scarab beetles, causing numerous holes in the leaves. From late July to early August, they will lay eggs and hatch white grubs that enter the surface soil layer under trees to damage lawn roots. If the population base is large, it may cause the death of entire lawns.
   (2) Azalea lace bug. The damage period of the azalea lace bug is from April to October. High temperature and dryness in July and August may cause an outbreak.
   (3) Red spider mite. Red spider mites occurring on roses are prone to outbreak in the cool season of May, while red spider mites occurring on camphor trees are different, being prone to outbreak in hot and dry seasons. Low rainfall during the plum rain season will cause a major outbreak of camphor red spider mites. After feeding, red spider mites cause leaf chlorosis, turning brown, which not only affects tree vigor but also affects the landscape.
   (4) Slug moths. Slug moths, commonly known as "yang la mao," have many species, mainly including yellow slug moth, green slug moth, blue slug moth, flat slug moth, etc. They mostly overwinter as larvae in cocoons. Young larvae cluster to feed on leaves and have an extremely wide range of damage, harming many garden plants such as Chinese wingnut, redleaf plum, camphor tree, photinia, and cherry blossoms. In severe cases, they can eat all the leaves, greatly affecting the landscape. They generally appear in mid-to-late June, with July to September being the most severe. In the early stage, they cluster on the underside of leaves to cause damage, so when spraying pesticides for control, attention should be paid to thoroughly spraying the underside of leaves.
   (5) Lawn noctuids. Lawn noctuids are mainly tobacco cutworms and silver-marked noctuids. They have already occurred in June. The high-temperature weather after the plum rain season may cause outbreaks of noctuids, so close attention should be paid to the occurrence of lawn noctuids. Once bald patches are found on the lawn, focused observation should be conducted, and timely control should be carried out if found. Due to their habit of hiding by day and coming out at night, the control time must be chosen after sunset.
   (6) Armyworms. They mainly damage lawns. This pest has a large appetite and causes damage rapidly. If not controlled in time, it can eat all the grass blades of a lawn in one night.
The early larval stage should be seized to control with Bt emulsion, diflubenzuron No. 1, or diflubenzuron No. 3.
   (7) Comstock mealybug. Comstock mealybug is also known as mulberry mealybug. At present, it occurs on a large scale on golden leaf privet in road isolation belts and residential areas in urban areas. The symptoms are often mistaken for leaf desiccation caused by exposure to sun and water shortage. Upon careful observation, white flocculent material can be found. Relevant units should pay sufficient attention and promptly carry out control.
   (8) In addition to the above main pests and diseases, attention should also be paid to controlling the poplar prominent moth (pyrethroids and BT); bagworms (diflubenzuron No. 3); blue willow leaf beetles on willow trees (BT); camphor nest borers occurring on some camphor trees (spray with BT (mie e ling) 500x solution, diflubenzuron No. 3 2000x solution, or ku yan emulsion 800x solution); leafhoppers on warm-season lawns (bermudagrass, tiantang grass, etc.), and box tree webworms on boxwood, etc.
   II. Main Diseases
   (1) Golden leaf privet leaf spot disease: Diseased leaves produce nearly circular brown lesions, often with concentric rings, and the outer edges are often yellow. In the early stage, the lesions are relatively small. After expansion, the lesions are more than 1 cm in diameter. Diseased leaves easily fall off from branches, causing the phenomenon of bare branches in severely affected areas of golden leaf privet. The first occurrence period is early April, with peak periods in July to August and October.
    (2) Silk tree wilt disease: In the early stage, leaves turn yellow, wilt and droop, and then dry up and fall off. In summer, branches become rough, and sometimes small black particles are produced. In severe cases, yellow leaves, dead branches, and bark rot occur, leading to the death of the entire plant.
   (3) Powdery mildew diseases: Mainly including poplar powdery mildew, large-leaf boxwood powdery mildew, crape myrtle powdery mildew, etc.

Garden Plant Pest and Disease Control Methods

(I) Nursery Stock Quarantine

Some pests and diseases have a relatively narrow distribution range and only cause serious harm in localized areas. However, these pests and diseases can spread to new areas along with the long-distance transportation of nursery stock seeds, cuttings or roots used as propagation material, logs, and other garden products, expanding their scope of harm. With social development, international or inter-regional personnel exchanges and product trade have become increasingly frequent, increasing opportunities for the spread of dangerous pests and diseases. For example, the fall webworm was introduced from abroad into Liaoning Province, then spread to Wugong County in Shaanxi Province via railway transportation, and entered Rongcheng County in Shandong Province via water routes. Therefore, strictly implementing China's quarantine regulations, carrying out import and export quarantine of nursery stock pests and diseases at airports, ports, stations, and other gateways for commodity import and export, and carrying out quarantine at nursery stock production sites and during transfer within the country to prevent problems before they occur, are important measures for controlling the expansion and spread of dangerous pests and diseases.

In 1996, China's Ministry of Forestry newly designated 35 domestic forest plant quarantine objects. They are Japanese pine bast scale, San Jose scale, slash pine mealybug, pine armored scale, larch seed chalcid, megastigmus seed chalcid, willow flat moth, double-hooked longhorned beetle, yellow-spotted longhorned beetle, rusty longhorned beetle, double-striped spruce longhorned beetle, fall webworm, poplar clearwing moth, poplar hidden-snout weevil, apple cotton aphid, codling moth, jujube giant scale, almond sawfly, pine wood nematode disease, pine blister rust, pine needle red band disease, pine needle brown spot disease, crown gall disease, poplar mosaic virus disease, larch shoot blight, moso bamboo shoot blight, Chinese fir top shrinkage disease, eucalyptus dieback disease, kiwifruit bacterial canker, cinnamon branch wilt disease, chestnut blight, carnation wilt disease, chrysanthemum leaf-killing nematode disease, citrus canker, etc. When quarantine objects are found during inspection, measures such as disinfection treatment, on-site burning, or isolation and trial planting of the inspected items should be taken promptly. Due to problems such as lax law enforcement and relatively backward detection methods and facilities in quarantine work, quarantine pests such as pine wood nematode disease, fall webworm, Japanese pine bast scale, pine armored scale, and poplar weevil are still spreading, which should attract high attention from relevant departments.

(II) Horticultural Techniques

Horticultural measures are fundamental measures for pest, disease, and rodent control and should run through the entire production process. The main measures include:

1. Select and breed excellent tree species with strong resistance to pests and diseases. Different tree species and different varieties of the same tree species have differences in resistance to various pests and diseases. If a variety only has fast-growing and high-yield characteristics but is not resistant to pests and diseases, it is difficult to promote it in production. For example, the Daguan poplar planted on a large scale in China in the 1970s was eliminated shortly after promotion due to damage by wood-boring pests such as the glossy longhorned beetle. This lesson illustrates the importance of pest and disease resistance breeding in control work. China's resistance breeding work started relatively late. Plant protection workers and breeding workers should strengthen collaboration to breed more excellent varieties with pest and disease resistance to meet production needs. At present, some excellent varieties or clones resistant to pine blister rust, poplar longhorned beetles, poplar canker, and paulownia witches' broom have been bred.

Some European and American countries have cultivated many excellent varieties with strong pest and disease resistance by utilizing the strong genetic plasticity of poplars. In 1988, American scientists achieved breakthrough progress in poplar insect resistance breeding using genetic engineering methods. Through gene splicing, they transferred the protein gene from potatoes that has an inhibitory effect on insects into poplars via Escherichia coli, cultivating a new type of insect-resistant tree species. Chinese breeding workers are also conducting research in this area.

2. Select different tree species and densities according to different site conditions.

3. Create mixed forests and avoid monoculture of tree species.

4. Use strong seedlings free of pests and diseases for afforestation.

5. Take measures such as cultivating, weeding, fertilizing, irrigating, and pruning to strengthen the management of young and middle-aged forests and promote plant growth.

6. Promptly remove diseased and pest-infested trees from the system to improve sanitary conditions.

7. Strictly prohibit indiscriminate felling and promote multi-layered vegetation growth.

Through the above measures, plants can grow robustly, resistance to pests and diseases can be enhanced, and various natural enemy insects, beneficial microorganisms, birds, and other natural enemies can increase significantly, thereby improving the control capacity of the entire plant system against pests and diseases. The improvement of horticultural environmental sanitation conditions reduces the population of pathogens and pests.

(III) Biological Control

Using beneficial organisms to control garden pests and diseases has advantages such as saving energy, lower control costs, no environmental pollution, and sustainable control effects. In the past ten years, biological control has received increasing attention and is worth vigorously promoting.

1. Microbial preparations. Microbial insecticides mainly include Beauveria bassiana, Bacillus thuringiensis, insect viruses, etc. China applies Beauveria bassiana over a relatively large area each year to control pine caterpillars. From 1984 to 1986, Hubei, Hunan, and Guangdong provinces applied Qingchongjun No. 6 liquid to control masson pine caterpillars over more than a thousand hectares, with an effectiveness of over 90%. Since the 1980s, China has used the spring cankerworm polyhedrosis virus, masson pine caterpillar cytoplasmic polyhedrosis virus, and gypsy moth nuclear polyhedrosis virus to control spring cankerworm, masson pine caterpillar, and gypsy moth, respectively, with promotion areas all above 6000 hm2. The use of Acremonium to control poplar weevil and the use of Taishan No. 1 nematode to control poplar longhorned beetles have also achieved obvious results. China's microbial preparations, especially Beauveria bassiana, rank among the world's leaders in both output and application area. However, because most microbial preparations are produced by traditional methods and no unified quality testing standards have been established nationwide, the quality of preparations cannot be guaranteed. Problems such as unstable effects and high costs have appeared during application, causing the application area of Beauveria bassiana in some provinces to decline year by year in recent years, and the application area of Bacillus thuringiensis is also not large.

The former Soviet Union, the United States, Canada, and other countries have produced a variety of registered commercial microbial preparations. In the former Soviet Union, the area of biological control accounted for more than 50% of the total national forest pest and disease control area each year. They mainly used Bacillus thuringiensis and polyhedrosis viruses to control leaf-eating pests such as gypsy moth, green oak tortrix, pine looper, and pine caterpillar, and Beauveria bassiana to control bark beetles. The area in the United States and Canada using Bacillus thuringiensis to control spruce budworm each year is about 105 hm2. Japan's red pine caterpillar cytoplasmic polyhedrosis virus (CPV) is the world's first registered and commercially produced virus preparation, used to control red pine caterpillar. The United States and Canada also produce a variety of virus preparations for controlling leaf-eating pests. Because virus preparations take effect slowly, adding a small amount of chemical pesticide can accelerate pest death and improve control effectiveness.

The United States, Australia, and other countries have already applied commercial microbial preparations in production to control crown gall disease and root rot. The use of powdery mildew parasitizing fungi can control powdery mildew, and rust parasitizing fungi can control the development of rust. The use of large-celled corticioid fungi controls pine silver-white rot, etc.

2. Natural enemy insects. The parasitic natural enemy insects widely used in China include Trichogramma, Sclerodermus, Eulophidae, Aphelinidae, and longhorned beetle parasitic ichneumon wasps, etc. Predatory natural enemy insects include Mongolian ladybird, harlequin ladybird, and ?? bugs, etc. From the late 1970s to the early 1980s, the area in China using Trichogramma to control pine caterpillars reached hundreds of thousands of hectares. Years of production practice have proven that artificial release of Trichogramma within a certain range is still a good method for controlling pine caterpillars under low pest population density conditions. At present, the application area is relatively large in Zhejiang, Hunan, and other provinces. The use of Mongolian ladybird to control pine bast scale, the use of parasitic natural enemies Puman to control concealed pests (such as Coleoptera longhorned beetles (double-striped spruce longhorned beetle), bark beetles (cypress bark beetle), bostrichid beetles (two-toothed stem borer), jewel beetles, and Lepidoptera pests such as pine shoot borers and six-spotted leopard moths), the use of Sclerodermus to control double-striped spruce longhorned beetle, thick-sheathed double-striped spruce longhorned beetle, and poplar longhorned beetle, the use of Chou's tussock moth parasitoid to control fall webworm, the use of flower-angle aphelinid wasp to control pine armored scale, and the use of longhorned beetle parasitic ichneumon wasps to control poplar longhorned beetle all have obvious effects. However, except for Trichogramma, other natural enemies have not been widely used in production because problems such as reproductive hosts, industrial production processes, or unstable control effects have not been fully solved. In addition to artificial release, attention should be paid in production to protecting the ecological environment of artificial forests and creating conditions for the reproduction of natural enemies, thereby improving the control effect of various natural enemy insects in nature on pests.

The United States pays great attention to introducing natural enemy insects from abroad and has achieved success in using introduced natural enemy insects to control pests such as larch casebearer. France's research on Trichogramma is at the world's forefront. Its Anglet biological control experimental station has collected Trichogramma from various countries around the world, conducted research in many aspects, and used them to control agricultural pests. The United States, the United Kingdom, the former Soviet Union, and other countries have also reported using Trichogramma to control spruce budworm, but because the control effect was not obvious, it was not widely used in production.

3. Beneficial birds. In poplar artificial forests, using artificial bird nests to attract beneficial birds such as great tits, woodpeckers, and gray-chinned minivets can significantly reduce the density of leaf-eating pests and wood-boring pests. According to observation, a pair of woodpeckers can control the glossy longhorned beetle in 20 to 30 hm2 of poplar forest. Owls also have an obvious control effect on forest rats.

Germany, the former Soviet Union, and other countries attach great importance to the protection of beneficial birds in artificial forests and research on techniques for artificially attracting beneficial birds. Because the forest stand ecological environment in these countries is relatively good, the role of beneficial birds in protecting forests is very obvious.

4. Application of sex pheromones. Since the 1970s, artificially synthesized sex pheromones have been used for forecasting and control of some pests. China has made traps using the sex pheromone of the poplar clearwing moth and the gypsy moth pheromone, and has achieved good results in trapping and killing poplar clearwing moths and gypsy moths.

(IV) Chemical Control

At present, chemical control is still the main measure for controlling major outbreaks of pests and diseases and eliminating pest source bases. China's chemical control area accounts for about 70% of the total forest disease and pest control area. On the premise of doing a good job in forecasting, correctly using pesticides for timely control can generally achieve good control results. Commonly used insecticides in China include avermectin, imidacloprid, fipronil, diflubenzuron, etc. Fungicides include chlorothalonil, carbendazim, triadimefon, and thiophanate. The main application methods include spraying, dusting, fumigation, seed dressing, and smoke generation. In recent years, the application of aircraft ultra-low-volume spraying technology has improved control effectiveness, saved labor, and reduced costs. In production, simple and easy application methods such as painting rings on tree trunks with poison pens, tying poison ropes or medicated paper strips, inserting poison sticks or medicine tablets into borer holes, injecting medicinal liquid, and spreading poisoned soil or bait have also been developed, achieving very good control results. Some pesticides with relatively low toxicity, such as chlordimeform, benomyl, thiophanate, and deltamethrin, are partly dependent on imports. Because pesticide prices are relatively high, aircraft control costs continue to rise, and ground sprayer spraying range is insufficient, control effectiveness has been affected. In some places, deltamethrin has been used alone for a long time, and pests have developed resistance, affecting the progress of chemical control work. It is worth mentioning that bamboo locusts, which had been eradicated with BHC powder in the 1950s and 1960s, showed signs of resurgence in the 1980s. One important reason is that no chemical agent has yet been found to replace BHC.

Fungicides can be divided into eradicants, protectants, and systemic fungicides. Eradicants can directly kill pathogens, such as pentachlorophenol and formaldehyde. Protectants can be directly applied to plant bodies to protect plants from invasion, such as low-concentration lime sulfur mixture, Bordeaux mixture, organic sulfur, organic phosphorus, and organic chlorine. Systemic fungicides refer to agents absorbed by plants that inhibit pathogen expansion, such as thiophanate, carbendazim, and benomyl. The use methods of chemical agents include soil disinfection, seed and fruit disinfection, and spraying plants.

However, the extensive use of chemical agents for control has produced serious "3R" problems, namely Resistance, Resurgence, and Residue. Many pests have developed resistance to chemical pesticides tens of times or even hundreds to thousands of times greater. The populations of some major pests sharply decline and then suddenly rebound, causing greater harm, and secondary pests suddenly outbreak after natural enemies are killed. Pesticides not only harm non-target species such as natural enemies, pollinating insects, and wildlife, but also seriously pollute soil, water bodies, the atmosphere, and animal and plant products, in turn causing new pest crises.

(V) Physical Control

In production, the phototaxis of some adult pests to light can be used by setting black light lamps or high-voltage insect-killing lamps to trap and kill adults. Methods such as ultrasound, heat treatment, and radiation irradiation can also be used to treat seeds and cuttings to eliminate pathogens or pests. For example, soaking paulownia seed roots in warm water at 47 to 51 degrees C for 1 hour can control paulownia witches' broom. In northern China, by utilizing the habit of pine caterpillars descending from trees to overwinter, plastic bands can be tied around tree trunks before pine caterpillars climb trees in spring, which can prevent overwintering larvae from climbing trees and reduce their damage.